1. Field of the Invention
The present invention relates to an automotive alternator and, more particularly, to an assembly structure of a rectifying unit for an automotive alternator.
2. Description of the Related Art
FIG. 11 is a perspective view showing a conventional rectifying unit applied to an automotive alternator. FIG. 12 is a sectional view of an essential section for explaining the conventional rectifying unit, which has been installed.
Referring to FIG. 11 and FIG. 12, a rectifying unit 120 includes a plurality of positive-electrode-side diodes 20 and negative-electrode-side diodes 21 for carrying out full-wave rectification on three-phase alternating current, a first cooling plate 122 and a second cooling plate 123 for cooling the positive-electrode-side diodes 20 and the negative-electrode-side diodes 21, respectively, insulators 24 and 27 for insulating the first and second cooling plates 122 and 123, a circuit board 125, and an output terminal 26. The positive-electrode-side diode 20 and the negative-electrode-side diode 21 constitute a first diode and a second diode, respectively.
The first cooling plate 122 is shaped like a horseshoe, and has the positive-electrode-side diodes 20 arranged on a main surface 122a thereof in the circumferential direction. A radiating fin 122b is vertically installed from the rear surface of the first cooling plate 122, that is, the surface opposing the main surface. Three flanges 130, 131, 132 are provided at both ends and the middle, respectively, in the circumferential direction of the first cooling plate 122. All the flanges 130, 131, and 132 are raised from a main surface 101a of the first cooling plate 101, and extended outward in the radial direction. An output terminal insertion through hole 134 is provided in the radially extended end of the flange 130 provided at one circumferential end of the first cooling plate 122. Mounting screw insertion through holes 133 are provided in the radially extended ends of the remaining flanges 131 and 132.
The second cooling plate 123, which is also shaped like a horseshoe, has a larger diameter than that of the first cooling plate 122, and has the negative-electrode-side diodes 21 arranged on a main surface 123a thereof in the circumferential direction. Furthermore, one output terminal insertion through hole 138, and two mounting screw insertion through holes 135 are provided at both ends and the middle in the circumferential direction of the second cooling plate 123 such that they align with the output terminal insertion through hole 134 and the mounting screw insertion through holes 133 provided in the first cooling plate 122, respectively.
The circuit board 125 is a resinous molding having insert-molded wiring for constituting diode bridges for the positive-electrode-side diodes 20 and the negative-electrode-side diodes 21, and horseshoe-shaped like the second cooling plate 123. Furthermore, one output terminal insertion through hole 137 and two mounting screw insertion through holes 136 are provided at both ends and the middle in the circumferential direction of the circuit board 125 such that they align with the output terminal insertion through hole 134 and the mounting screw insertion through holes 133 provided in the first cooling plate 122, respectively.
Each of the cylindrically shaped insulators 24 is made of, for example, a phenol resin, and has a flange 24a in the central portion of the outer periphery thereof. The cylindrically shaped insulator 27 is made of, for example, a phenol resin, and has a flange 27a at one end portion thereof. The output terminal 26 has a knurl groove portion 26a provided at the counter-takeout side and an external thread portion 26b provided at the takeout side.
The rectifying unit 120 is assembled as described below. First, the insulators 24 are inserted in the mounting screw insertion through holes 135 of the second cooling plate 123 such that the flanges 24a are in contact with the main surface 123a. Similarly, the insulator 27 is inserted in the output terminal insertion through hole 138 of the second cooling plate 123 such that the flange 27a is in contact with the main surface 123a. Then, the first cooling plate 122 is disposed such that the insulators 24 are inserted in the mounting screw insertion through holes 133. This concentrically arranges the first and second cooling plates 122 and 123, respectively, with their main surfaces 122a and 123a being flush with each other, and the positive-electrode-side diodes 20 and the negative-electrode-side diodes 21 facing each other. The circuit board 125 is stacked on the main surface 123a of the second cooling plate 123 such that the insulators 24 are inserted in the mounting screw insertion through holes 136. Thus, connecting terminals 125a of the circuit board 125 are held between terminals 20a and 21a of the opposing positive-electrode-side and negative-electrode-side diodes 20 and 21, respectively, and joined by soldering. Subsequently, the output terminal 26 is inserted from the output terminal insertion through hole 137 of the circuit board 125 into the output terminal insertion through holes 134 and 138 of the first and second cooling plates 122 and 123, respectively. Lastly, the knurl groove portion 26a of the output terminal 26 is press-fitted into the output terminal insertion through hole 134 of the first cooling plate 122 to electrically connect the output terminal 26 and the first cooling plate 122, completing the assembly of the rectifying unit 120 shown in FIG. 11.
In the rectifying unit 120 assembled as described above, a mounting screw 40 inserted in the mounting screw insertion through holes 133, 135, and 136 is fastened into a tapped hole 2a provided in a rear bracket 2 so as to fasten together the first and second cooling plates 122 and 123, and the circuit board 125, as illustrated in FIG. 12. The takeout end of the output terminal 26 connected to the first cooling plate 122 is extended out of an opening 2b provided in the rear bracket 2. An output terminal fastening nut 50 threaded to the external thread portion 26b of the output terminal 26 is fastened thereby to fasten together an insulating bush 41 formed of a phenol resin mounted on the opening 2b of the bracket 2, the first and second cooling plates 122 and 123, and the circuit board 125 onto the rear bracket 2.
To join a vehicular connecting terminal 42 to the output terminal 26, the connecting terminal 42 is externally fitted to the takeout end of the output terminal 26, and a nut 44 is screwed onto the external thread portion 26b. Then, the nut 44 is tightened to fasteningly secure the connecting terminal 42 to the outer end surface of the nut 50. In this case the outer end surface of the output terminal fastening nut 50 serves as a fastening seat.
The first and second cooling plates 122 and 123, the circuit board 125, and the insulating bush 41 are secured together to the rear bracket 2 by the fastening force of the output terminal fastening nut 50. With this arrangement, even if the vibration caused by a weight, such as a harness, is transmitted from the vehicle to the vehicular connecting terminal 42, the output terminal 26 will not be displaced in the axial direction, thus initially preventing damage or the like to the rectifying unit 120. Moreover, since the fastening force of the nut 44 is received by the outer end surface of the output terminal fastening nut 50 making up the fastening seat, the fastening force for the vehicular connecting terminal 42 is initially secured.
In the conventional automotive alternator, since the rectifying unit 120 is assembled and installed as set forth above, when power is generated by the automotive alternator, large current passes the vehicular connecting terminal 42, generating heat. The generated heat is conducted from the nut 50 to the insulating bush 41, and the insulating bush 41 becomes hot. This has been posing a problem in that the insulating bush 41 develops thermal degradation and shrinks. The shrinkage of the insulating bush 41 causes loose fastening by the output terminal fastening nut 50, allowing the output terminal 26 to be displaced in the axial direction. As a result, if the vibration of a weight, such as a harness, from a vehicle is transmitted to the vehicular connecting terminal 42, the output terminal 26 is displaced in the axial direction. This has been giving a rise to a problem in that the rectifying unit 120 may be damaged or the fastened portion of the mounting screw 40 may break, with consequent degraded reliability.
If the output terminal fastening nut 50 loosens, then the connecting terminal 42 fastened by the nut 44 accordingly becomes loose. This causes markedly increased heat generation at the fastened portion of the connecting terminal 42, adding to the shrinkage of the insulating bush 41 attributed to thermal degradation. Hence, the output terminal 26 tends to be axially displaced more readily, leading to a problem in that the rectifying unit 120 is damaged or the fastened portion of the mounting screw 40 breaks more easily due to the vibrations caused by a weight, such as a harness, from a vehicle, resulting in degraded reliability.
Furthermore, the fastening force of the nut 44 is received by the output terminal fastening nut 50 pushing the insulating bush 41, posing a problem in that the vibration of a weight, such as a hardness, from a vehicle is repeatedly applied to the insulating bush 41 via the nut 50, causing the insulating bush 41 to develop a creep. The creep of the insulating bush 41 in turn leads to loose fastening by the output terminal fastening nut 50, giving a rise to the problem described above.
Accordingly, the present invention has been made with a view toward solving the problems described above, and it is an object of the present invention to provide an automotive alternator having an axial displacement restricting member for restricting the axial displacement of an output terminal connected to a first cooling plate of a rectifying unit, wherein a fastening seat for fastening a vehicular connecting terminal is provided at a takeout end of the output terminal to restrain damage to the rectifying unit attributable to the axial displacement of the output terminal and to restrain heat generation attributable to loosening of a fastened portion of the vehicular connecting terminal, thereby achieving improved reliability of the automotive alternator.
It is another object of the present invention to provide an automotive alternator wherein a fastening seat for fastening a vehicular connecting terminal, which is irrelevant to a fixing device, is provided at a takeout end of an output terminal by which first and second cooling plates of a rectifying unit are secured to a bracket, thereby restraining heat generation attributable to loosening of a fastened portion of the vehicular connecting terminal so as to achieve improved reliability of the automotive alternator.
To these ends, according to one aspect of the present invention, there is provided an automotive alternator including a rotor rotatably supported in a metal bracket, a stator secured to the bracket such that it is located around the outer periphery of the rotor to surround the rotor, a rectifying unit having a first cooling plate on which a plurality of first diodes are provided, and a second cooling plate on which a plurality of second diodes of the opposite polarity from that of the first diodes are provided, the second cooling plate being electrically connected to the bracket, and the first and second cooling plates being secured to an inner wall surface of the bracket, a resinous insulating bush mounted at an opening provided in the bracket, an output terminal which is electrically connected to the first cooling plate, loosely inserted in the insulating bush, and taken out of the bracket, a vehicular connecting terminal being connected to the takeout end of the output terminal, an axial displacement restricting member which engages the insulating bush thereby to restrict the axial displacement of the output terminal, and constitutes a fastening seat, and an external thread portion provided on the takeout end of the output terminal, wherein the counter-takeout end of the output terminal is secured to the first cooling plate, and the vehicular connecting terminal is fasteningly secured to the fastening seat of the axial displacement restricting member by a nut threadably attached to the external thread portion.
Preferably, an elastic member is interposed between the axial displacement restricting member and the insulating bush.
Preferably, the insulating bush is mounted at the opening of the bracket such that it is abutted against the axial displacement restricting member, and the insulating bush is formed of an elastic material.
Alternatively, the axial displacement restricting member is externally fitted to the output terminal, and composed of a cylindrical metal bush having a flange of a large diameter on one end thereof, one end surface of the metal bush abuts against the vehicular connecting terminal, and the other end surface thereof abuts against the first cooling plate, and the flange thereof engages the insulating bush to restrain the axial displacement of the output terminal when the vehicular connecting terminal is connected to the takeout end of the output terminal.
Alternatively, the axial displacement restricting member is constructed by a metal bush fastening nut threadably attached to the external thread portion of the output terminal, a cylindrical metal bush which is externally fitted to the output terminal and fasteningly secured to the first cooling plate by the metal bush fastening nut, the vehicular connecting terminal is fasteningly secured to the outer end surface of the metal bush fastening nut by the nut threadably attached to the external thread portion, and the inner end surface of the metal bush fastening nut engages the insulating bush thereby to restrain the axial displacement of the output terminal.
Preferably, the axial displacement restricting member is constituted by a large-diameter flange formed at the proximal end of the external thread portion of the output terminal, the vehicular connecting terminal is fasteningly secured to the outer end surface of the flange by the nut threadably attached to the external thread portion, and the inner end surface of the flange engages the insulating bush thereby to restrain the axial displacement of the output terminal.
Preferably, a support wall is vertically provided such that it opposes the counter-takeout end surface of the output terminal, and an insulating member is interposed between the support wall and the counter-takeout end surface of the output terminal.
According to another aspect of the present invention, there is provided an automotive alternator including a rotor rotatably supported in a metal bracket, a stator secured to the bracket such that it is located around the outer periphery of the rotor to surround the rotor, a rectifying unit having a first cooling plate on which a plurality of first diodes are provided, and a second cooling plate on which a plurality of second diodes of the opposite polarity from that of the first diodes are provided, the second cooling plate being electrically connected to the bracket, and the first and second cooling plates being secured to an inner wall surface of the bracket, a resinous insulating bush mounted at an opening provided in the bracket, an output terminal which is electrically connected to the first cooling plate, loosely inserted in the insulating bush, and taken out of the bracket, a vehicular connecting terminal being connected to the takeout end of the output terminal, through holes which are provided in the first and second cooling plates and in which the output terminal is inserted, an external thread portion provided on the takeout end of the output terminal, an output terminal fastening nut threadably attached to the external thread portion to fasteningly secure the output terminal to the bracket, and a fastening seat provided at a position different from that of the output terminal fastening nut on the takeout end of the output terminal, wherein the counter-takeout end of the output terminal is inserted in the through holes of the first and second cooling plates and secured to the first cooling plate, the first and second cooling plates are secured together with the insulating bush to the bracket by the output terminal fastening nut, and the vehicular connecting terminal is fasteningly secured to the fastening seat by a nut threadably attached to the external thread portion.
Preferably, the external thread portion of the output terminal is composed of a first external thread portion having a large diameter to which the output terminal fastening nut is threadably attached and a second external thread portion having a small diameter which is continuously formed at the takeout end of the first external thread portion and to which the nut is threadably attached, and a stepped portion formed in the area, where the first and second external thread portions are connected, constitutes the fastening seat.